JPH02247553A - Small-sized oxygen electrode - Google Patents

Abstract

PURPOSE:To electrochemically make stricter measurement by determining oxygen by 3-electrode constitution consisting of a working electrode, counter electrode and reference electrode. CONSTITUTION:A silicon oxide film 2 is deposited as an insulating layer over the entire surface of holes 5 formed by anisotropic etching in a silicon substrate 2 and further, the rear surface of the substrate 1 is coated with a hydrophobic insulating film 7. A part of a counter electrode 3B deposited in the holes 5 extends to the outer side of the holes 5 so as to be electrically connected to the outside and an electrolyte-contg. gel 6 is filled in the holes 5. Resist patterns 9 are provided in electrode sensitive parts and the part where there are no holes 5 formed with the working electrode 3A and the reference electrode 3C is acted to store the gel 6. A gas permeable film 14 covers the entire upper part of the substrate 1 to prevent the leakage of the gel 6 and simultaneously covers the side faces and rear surface of the substrate 1 as the insulating film. If the measurement is made by such 3-electrode constitution, current hardly flows in the electrode 3C and, therefore, the life thereof is prolonged and the there is eventually the effect of prolonging the life of the device itself. In addition, the stricter measurement is electrochemically made.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a small oxygen electrode, which consists of three electrodes consisting of a working electrode, a counter electrode, and a reference electrode, which enables precise electrochemical measurements and has the effect of extending the lifespan. The purpose is to provide a certain small-sized oxygen electrode, which includes a semiconductor substrate having a groove (hole) formed by anisotropic etching, an insulating film covering the surface of the substrate, and an insulating film extending from the bottom of the substrate to the surface of the substrate. a hydrophobic part defining an electrode sensitive part so as to provide a counter electrode, a working electrode and a reference electrode formed on the surface of the substrate in which the hole is not formed, and an internal electrolyte spanning over the counter electrode 1 working electrode and reference electrode; an electrolytic solution-containing porous material that covers the counter electrode, the two working electrodes and the reference electrode, and that includes the inside of the electrode and fills the electrode sensitive part, and a gas permeable film that covers the electrolytic solution-containing porous material. and constitute a small oxygen electrode.

[Industrial application field]

Small oxygen electrodes can be advantageously used for measuring dissolved oxygen concentrations in various fields.

For example, from the viewpoint of water quality conservation, biochemical oxygen demand f in water
1 (BOD) is being measured, and this small oxygen electrode can be used as a measuring device for the dissolved oxygen concentration. In addition, in the fermentation industry, it is necessary to adjust the dissolved oxygen concentration in the fermenter in order to proceed with efficient alcohol fermentation, and the small oxygen electrode of the present invention can be used as a measuring instrument for this purpose. The oxygen electrode can be combined with 2 enzymes to form an enzyme electrode, which can also be used to measure the concentration of 1!, vitamins, etc. 0 For example, glucose reacts with dissolved oxygen using the enzyme glucose oxidase as a catalyst to produce gluconolactone. However, by utilizing the fact that dissolved oxygen that diffuses into the oxygen electrode cell decreases, the glucose concentration can be measured from the amount of dissolved oxygen consumed.

In this way, the small oxygen electrode of the present invention is suitable for environmental measurement.

It can be used in various fields such as fermentation industry and clinical medicine, but especially in the field of clinical medicine where it is attached to a catheter and inserted into the body.

If it is small, disposable, and inexpensive, it is very useful.

[Conventional technology] The inventors found that with conventional glass oxygen electrodes.

Since miniaturization and mass production were not possible, we developed a new type of compact oxygen electrode using lithography technology and anisotropic etching technology, and applied for a patent (Japanese Patent Laid-Open No. 63-238548). In this method, two electrodes are formed on a hole formed by anisotropic etching on a silicon substrate through an insulating film, an electrolyte-containing body is housed inside the hole, and the upper surface of the hole is This is an oxygen electrode that has a structure covered with a gas permeable membrane. This oxygen electrode is small, has little variation in characteristics, and can be mass-produced in bulk, resulting in low cost.

The present inventors conducted research to further improve this point and make it more suitable for mass production. Using polyacrylamide gel, -
We discovered a method that allows gel to be injected all at once (Japanese Patent Application Laid-open No. 1983-
311158) The manufacturing method of this small oxygen electrode is as follows:
After forming multiple holes using lithography technology and anisotropic etching technology, electrodes were formed on each silicon substrate through an insulating film, and then a negative resist was coated on the silicon substrate, except for the large part. , the substrate is immersed in a solution of a photopolymerizable monomer, preferably acrylamide, containing an electrolytic solution, and each hole is filled with the solution and cured by irradiation with ultraviolet rays to form a porous carrier containing an electrolytic solution. is formed in a hole. According to this manufacturing method, it is possible to form a porous carrier that selectively retains the electrolyte only in the minute holes that form the small oxygen electrode, making mass production possible.

[Problem to be solved by the invention]

The method described in Japanese Patent Application Laid-Open No. 63-238548 mentioned above is an epoch-making manufacturing method in that very small oxygen electrodes can be produced in large quantities. However, a detailed study of this method revealed that there are problems that must be resolved before it can be put into practical use.

The small oxygen electrode according to the present invention is a small oxygen electrode that is mass-produced using lithography technology and thin film formation technology that are used for forming semiconductor integrated circuits. It must be possible to obtain a product with low nuisance and good reproducibility. One possible means for this is to replace the anode with a tffi/silver chloride reference electrode to more stably determine the potential for oxygen reduction at the cathode. , also devised one using a silver/silver chloride reference electrode for the anode (Japanese Patent Application Laid-Open No. 63-238548).
When this silver/silver chloride reference electrode is formed by lithography in the form of a thin film such as that used in the process of small oxygen electrodes, and when used in a two-bridge format with this reference electrode as an anode, the anode is completely chlorinated. The problem was that it turned into silver, making it more unstable than with gold anodes.

The instability in properties is due to the change of the 1i1/silver chloride reference electrode over time. In order to simplify the oxygen electrode as much as possible, the oxygen electrode has a structure consisting of only two cathodes and an anode.

[Means to solve the problem]

If electrochemical measurements are to be carried out more precisely, it is desirable to have a three-electrode configuration consisting of a working electrode that detects oxygen, a counter electrode, and a reference electrode.The three-electrode configuration is not only important for accuracy. With this configuration, the potential of one working electrode (cathode) is set constant with respect to the reference electrode, but the current mainly flows between the working electrode (cathode) and the opposite electrode (anode), and on the reference bridge, the composition is This is because electrochemical reactions that cause changes are unlikely to occur. For this reason, in order to solve the above-mentioned problems, it is more advantageous to adopt a three-pole configuration.

The present invention has been accomplished up to the above point, and includes a semiconductor substrate having a groove (hole) formed by anisotropic etching, an insulating film covering the surface of the substrate, and a surface of the substrate extending from the bottom of the substrate. The opposite pole was formed.

A working electrode and a reference electrode formed on the surface of the substrate in which the hole is not formed, and a hydrophobic insulating film defining an electrode sensitive part so as to provide an internal electrolyte spanning over the two counter electrodes and the working electrode and the reference electrode; A small oxygen having an electrolyte-containing porous material that covers the counter electrode 1 working electrode and the reference electrode and that includes the large interior and fills the electrode sensitive part, and a gas permeable membrane that covers the electrolyte-containing porous material. This is achieved by electrodes.

The electrode configuration of a small oxygen electrode is such that the area of the counter electrode is about 10 times the area of the working electrode, and the area of the counter electrode (anode) is large and the area of the working electrode (cathode) is small so that the counter electrode does not become rate limiting. is desirable from the viewpoint of electrical characteristics.

Therefore, as for the electrode configuration arrangement of the above-mentioned small oxygen electrode, the counter electrode (anode) is formed in a U-shape, and the working electrode (cathode) is formed complementary to the open part of the U-shape, as shown in the examples described later. Preferably, the reference electrode is arranged approximately symmetrically between the counter electrode and the working electrode. However, the electrode configuration is not limited to the above. Even if the 1t8i configuration arrangement is asymmetrical, it is sufficient that the electrolyte-containing porous material straddles the counter electrode 1 working electrode and the reference electrode and covers the electrode sensitive part.

The above-mentioned small oxygen electrode is made by forming a groove (hole) on a semiconductor substrate by anisotropic etching and forming an insulating film. A working electrode (cathode) and a reference electrode are formed on the surface of the substrate where no After forming the membrane, the gas permeable membrane is formed by filling the inside of the hole with an electrolyte-containing porous material so as to cover the exposed portions of the counter electrode 5 working electrode and reference electrode, and covering the electrolyte-containing porous material. It can be manufactured by

In carrying out the method of the invention, a semiconductor substrate, in particular a silicon substrate, can advantageously be used as the base material of the electrode body. The insulating film can be formed from a silicon oxide film or other materials.

A silicon oxide film can be easily formed by thermally oxidizing the substrate, for example, when the substrate is made of silicon.

A gold electrode or a platinum electrode can be used as the working electrode and counter electrode.

The photoresist coated on the substrate after electrode formation except for the hole portions and the portions for electrical contact is preferably a negative photoresist, such as OMR-8 manufactured by Tokyo Ohka Chemical Co., Ltd.
It is 3. This type of photoresist is advantageous because it has the property of repelling the aqueous solution that is the raw material when only the hole portions are filled with an electrolyte-containing porous material.

Formation of electrolyte-containing gel is described in 1, for example, JP-A-63-3111.
As described in No. 58, a substrate is immersed in an acrylamide aqueous solution containing an electrolyte, the substrate is slowly pulled up while immersed in such solution, and the substrate in this state is further irradiated with ultraviolet rays to gel it. Method and patent application 1986-1
This can be carried out advantageously by the method using calcium alginate as described in No. 76978. That is, polyacrylamide gel or calcium alginate gel can be used as the electrolyte-containing porous material. Moreover, a polymer electrolyte can be used instead of the electrolyte-containing porous material.

Various electrolytes such as potassium chloride and sodium sulfate can be used as the electrolyte to be retained by the porous carrier. Potassium chloride can be used as the electrolyte and a silver/silver chloride electrode can be used as the reference electrode.

Gas-permeable membranes are hydrophobic and do not allow aqueous solutions to pass through them, but they are initially liquid and can be dip-coated or spin-coated.
It is also essential that the adhesion between the silicon substrate and the silicon oxide film as an insulating film is good and that the electrolyte does not leak outside.

Suitable gas permeable membrane materials include photoresists, preferably negative-tone photoresists, and the like. Although Teflon (trade name) [1] is oxygen permeable, it does not have adhesive strength, so its use must be avoided.

[Effect]

If measurement is performed in the three-electrode format as described above, it becomes difficult for current to flow through the reference electrode, which has the effect of extending the life of the reference electrode and, by extension, the life of the small oxygen electrode itself. Also,
The three-electrode format has the effect of enabling more precise electrochemical measurements.

〔Example〕

A preferred example of the method for manufacturing a small oxygen electrode according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a plan view (A) showing a preferable example of a small-sized oxygen electrode according to the present invention, and a sectional view (B) of a sensitive part showing a section taken along the line ■--■ of the plan view (A). The oxygen electrode shown has a rectangular parallelepiped shape, and the sensitive part has gas permeability M! Along with being covered with 14.

1 working electrode 3A, counter electrode 3B for connecting to the attached device
, a part of the reference electrode 3C is exposed. In the case of five electrodes, electrodes 3A and 3B were gold electrodes, and electrode 3C was an iI/silver chloride reference electrode.

The silicon substrate 1 has a groove (hole) formed by anisotropic etching, and a silicon oxide film 2 is deposited as an insulating film on the entire surface thereof. Furthermore, the back surface of the substrate is covered with a hydrophobic insulating film 7 that is hard to tear. A counter electrode 3B is attached to the hole 5 of the silicon substrate 1.

On the other end of the spectrum is 3B.

As shown in FIG. 1, a portion extends outside the hole to make electrical contact with the outside. Further, the holes 5 in the silicon substrate 1 are filled with an electrolyte-containing gel 6. The electrode sensitive part.

This resist pattern 9 (FIG. 2(C)) is determined by patterning a negative photoresist.
This works advantageously to store electrolyte in the area where the hole in FIG. 1 where the working rod and reference electrode are formed is not dug. On top of the electrolyte-containing gel 6 filled in the hole, a gas permeable film 1 is placed so as to cover the entire upper surface of the substrate l (excluding the exposed part in FIG. 1).
4 is coated, and the side and back surfaces are also covered as an insulating film.

The miniature oxygen electrode shown in FIG. 1 can be advantageously manufactured, for example, by the manufacturing process shown in sequence in FIG. Note that the working electrode 3A and counter electrode 3B shown in FIG. 2(A)
The formed main body can be manufactured through the following steps. In the following explanation, in order to make it easier to understand, we will describe the case where only one oxygen electrode is formed on one wafer, but it is important to note that in reality, many small oxygen electrodes are formed at the same time. I want to be understood,
Furthermore, here, based on Japanese Patent Application No. 176978/1983,
The case where calcium alginate gel is used as an electrolyte-containing gel will be described.

(2) Wafer Cleaning A 2-inch (100)-sided silicon wafer with a thickness of 350II11 was prepared and cleaned with a mixed solution of hydrogen peroxide and ammonia and concentrated nitric acid.

2. Formation of SiO□ film A silicon wafer was subjected to wet thermal oxidation to form a SiOg film with a thickness of 0.8 μ- on the entire surface.

3. Formation of etching pattern An etching resist pattern was formed on the wafer using a negative photoresist (Tokyo Ohka OMR-83, viscosity 60 cP).

4. Coating of resist for backside protection The same negative photoresist as used in the above step was also applied to the backside of the wafer and baked at 130°C for 30 minutes.

Etching of 5,5iOz film 50% hydrofluoric acid: 40% ammonium fluoride = l:
The wafer was immersed in a 6 aqueous solution, and the exposed portions 5i (h) not covered with photoresist were removed by etching. Subsequently, the resist was removed with a sulfuric acid/hydrogen peroxide solution (2:1).

6. Anisotropic etching of Si Anisotropic etching of silicon was performed in a 35% potassium hydroxide aqueous solution at 80°C. Etching depth 300
After completion of etching, the wafer was washed with pure water.

After completing this anisotropic etching, the SlO□ film used during etching was removed. This was carried out in an aqueous solution of 0% hydrogen fluoride M:40% ammonium fluoride=lj6 as in 5.

7.5IOJ! Formation In order to grow a SlO□ film on the silicon wafer surface,
Following the cleaning step of 1, the wafer was wet thermally oxidized. A film with a thickness of 0.8 pm was formed.

8. Formation of Chromium and Gold Thin Films Following the ROM thin film (400 people, adhesion of gold and substrate), a gold thin film (4000 people) was formed by vacuum evaporation.

9. Formation of resist pattern for forming working electrode/counter electrode Negative photoresist (Tokyo Ohka type OMR-83° viscosity 60
cP) is used to place a working electrode on the ^um film of the wafer.
A resist pattern for forming a counter electrode was formed.

IO8 The substrate on which the gold and chromium etching resist pattern has been formed is immersed in the following gold and chromium etching solutions in this order, and the exposed gold and chromium parts are removed by etching. Furthermore, after washing with pure water, sulfuric acid/hydrogen peroxide solution (2:1)
The resist was removed using a solution (FIG. 2(A)).

■Gold etching liquid: 4gK! and l g I! ■ Chrome etching solution 20.5 g NaOH and 1
g KsPe(CN)i dissolved in 4 ml of water 11. Formation of chromium and m thin films Following ROM thin film (400 people, adhesion of silver and substrate), l! Thin films (4000) were formed by vacuum evaporation.

12. Formation of silver chloride layer: 0. Formation of silver chloride layer. Soak in IMKCl.

A voltage of +1.0 V was applied between the silver plate and the platinum plate to form a silver chloride layer on the silver surface.

13. Formation of resist pattern for reference electrode formation Positive photoresist (Tokyo Ohka type 0FPR-800° viscosity 20
cP) and spread it evenly over the wafer. The amount of resist should be just enough to cover the wafer; spin coating is not possible. 80
The film thickness of the positive photoresist, which was post-baked at .degree. C. for 30 minutes, was different between the inside of the groove and the flat part, but was formed so that the film thickness of the flat part was several tens of microns.

After aligning the patterns with an aligner and performing exposure, one development is performed, rinsed with water, and dried. As in this example,
If the positive photoresist is applied thickly,
- It is not exposed to light, and once the exposed area is removed to a certain depth, development will no longer proceed. Therefore, the aligner
After aligning the photomask pattern with the resist pattern in the middle of development and performing exposure, development, rinsing, and drying are performed again.

Once the substrate surface has been completely developed, proceed to the next step.
If the exposure is still incomplete, repeat exposure, development, rinsing, and drying. A positive resist pattern remains only where the silver pattern will ultimately be formed.

The substrate on which the 14° silver and chromium etching resist pattern has been formed is immersed in the following silver and chromium etching solutions in this order, and the exposed silver and chromium portions are removed by etching. Furthermore, after washing with pure water, sulfuric acid/hydrogen peroxide solution (2:1)
Remove the resist with a solution.

■Etching solution = 29z ammonia water: 31x hydrogen peroxide water; water 1:1:20 solution.

■Chrome etching liquid: 0.5 g Na0II
Figure 2 shows the completed state of the working electrode, counter electrode, and reference electrode by dissolving 1 g of K3Fe(CM)h in 4 ml of water.
Shown in B).

15. Formation of resist pattern for gel injection (Figure 2 (C)
) On the surface of the main body, apply negative photoresist (Tokyo Ohka
This was done by applying photoresist to the surface of the wafer and exposing and developing after 1 blubrator. The film thickness of the photoresist that defines the sensitive area at the flat part is several βm.
It is.

Incidentally, as a matter of course, the exposure and development is performed using a mask that does not leave any resist film on the scribe line, which is the cutout portion of the substrate.

16. Hydrophobic insulation film formed on the back side of the substrate Hydrophobic insulation II (ES-1 made by Shin-Etsu Silicone) was formed on the back side of the substrate.
001) on - birch and baked at 150'C for 1 hour.

17. Cutting out the substrate A large number of oxygen electrodes formed on the substrate were cut into chips.

18. Filling of Calcium Alginate Gel The following two types of solutions were prepared for forming electrolyte-containing gels.

Solution A: Sodium nyalginate dissolved in 0.1 M potassium chloride aqueous solution. Sodium alginate concentration 0
．． 2χ.

Solution B: Calcium chloride dissolved in 0.1M potassium chloride aqueous solution, calcium chloride concentration 5%.

When the chip shown in FIG. 2(C) was immersed in liquid A and slowly pulled up, the negative photoresist film 9 was hydrophobic, so the previous liquid A was repelled from the resist film and contained the inside of the hole 5 and the opposite electrode. 3B, a working electrode 3A, and a reference electrode 3C were formed and remained only in the electric bridge sensitive area defined by the photoresist film 9. Then, when this chip was immersed in Solution B, Solution A instantly gelled.

19. Covering the gas-permeable membrane (Fig. 2 (D)) The gas-permeable membrane 14 is coated on the electrolyte-containing gel 6 so as to cover the gel.
In this example, the same negative photoresist as used in step 3 was used as the gas permeable film. That is, negative photoresist (Tokyo Ohka OMR-
83 (trade name) (viscosity 60 cP) was applied by dip coating. This resist is immediately exposed to light without pre-bathing, and then the small oxygen electrode body is left in pure water or saturated steam overnight to draw out the thinner in the resist, and the gas permeable film and sidewall insulating film are completed. Ta. This resist film is also formed on the back surface, which has an advantageous effect in further improving the insulation properties.

〔Effect of the invention〕

According to the method of the present invention, there are three electrodes consisting of one working electrode, one counter electrode, and one reference electrode.
Oxygen can be quantified using a polar configuration, which not only allows for more precise electrochemical measurements.

Unlike the two-rod configuration, damage to the reference pole can be suppressed.

Only the counter electrode (anode) is formed from within the groove (hole) formed by anisotropic etching to the surface of the substrate, and the working electrode (cathode) and reference electrode are formed on the surface of the substrate where no groove is formed. It is possible to increase the area facing the sun, and
Formation of the reference pole becomes easier.

[Brief explanation of drawings]

Figure 1 is a plan view (A) and a cross-sectional view of the sensitive part (B) showing a preferable example of a small oxygen electrode based on a zero source, and Figures 2 (A) to (D) are the same as those shown in Figure 1. FIG. 3 is a cross-sectional view sequentially showing the latter half of the manufacturing process of a small oxygen electrode. In the figure, l is a substrate, 2 is an insulating film, and 3A is a working electrode. 3B is a counter electrode, 3C is a reference electrode, 5 is a hole, 6 is an electrolyte-containing gel, 7 is a hydrophobic insulating film, 9 is a resist pattern, and 14 is a gas permeable film. 4 coins (AI plan drawing CΔ) (E) C (D) Child drawing

Claims (1)

[Claims] A semiconductor substrate having a groove (hole) formed by anisotropic etching, an insulating film covering the surface of the substrate, a counter electrode formed from the bottom of the hole to the surface of the substrate, and a counter electrode in which the hole is not formed. a working electrode and a reference electrode formed on the surface of the substrate, and a hydrophobic insulating film defining an electrode sensitive part so as to provide an internal electrolyte spanning over the counter electrode, the working electrode, and the reference electrode;
An electrolyte-containing porous material covering the working electrode, counter electrode, and reference electrode and filling the electrode sensitive part including the inside of the hole, and a gas permeable membrane covering the electrolyte-containing porous material. Features a small oxygen electrode.